The information about head motion and orientation provided by the vestibular labyrinth is constrained by several features, but the brain is still able to generate relatively accurate perceptual and eye movement responses during vestibular stimulation. One major problem the vestibular system must deal with is the noise inherent in all aspects of neural processing. In this proposal we will use several novel techniques (including vestibular psychophysics in non-human primates, high-frequency electrical stimulation of semicircular canal afferents, and measures of the vestibulo-ocular reflex (VOR) threshold and central vestibular noise) to investigate how noise affects the central processing that is responsible for vestibular-mediated eye movement and perceptual responses. More specifically, we propose three hypotheses which we will test in three specific aims that focus on the brain's ability to optimize perceptual and eye movement responses despite the limitations in the information provided by the labyrinth. In the first two specific aims, we will vary the amount of noise on the canal afferent signals by using very high-frequency electrical stimulation of the canal ampullary nerves superimposed on the normal canal afferent cues. We will investigate how noise on the canal rotational inputs affects perceptual and eye movement responses, and predict that when the noise increases the velocity storage integrator in the brain will become less effective (aim 1) and that the misperception of low-frequency translation as tilt will be accentuated (aim 2). In specific aim 3, we will investigate the hypothesis that peripheral vestibular ablation increases central vestibular noise by inducing different degrees of peripheral vestibular hypofunction with aminoglycosides and measuring changes in the VOR and in a behavioral measure of vestibular noise, based on changes in the variance of eye velocity during fixation of a punctate target with the head stationary. In sum, these experiments will help answer longstanding and fundamental questions about how vestibular information is processed centrally, and this work will not only improve understanding of normal vestibular physiology but may also help elucidate the mechanisms responsible for the abnormal perceptual and eye movement responses that occur with disorders of the peripheral and central vestibular system.